JP6660282B2 - Light receiving element - Google Patents

Description

  The present invention relates to a structure of a light receiving element for optical communication.

  Conventionally, a photodiode (PD), which is an optical semiconductor element, is used as a light receiving element in a receiving module for optical communication. However, in response to an increase in communication capacity in recent years, a PD is required to have a high-speed response characteristic. It has become.

  As one of means for responding to the high-speed response of the PD, it is generally performed to reduce the junction area of the PD to reduce the junction capacitance.

  However, reducing the bonding area is equivalent to reducing the area (light receiving area) that can absorb light as a PD. Therefore, reducing the bonding area reduces the efficiency of optical coupling with signal light and reduces reception. This leads to lower mounting tolerance when mounting as a module.

In order to alleviate this relationship, as shown in the conventional example of FIG. 1, a lens is integrated on the back surface of the PD and the signal light incident from the back surface is condensed, so that the optical coupling efficiency is small even if the junction area is small. There has been realized a light receiving element having a structure capable of reducing the reduction in mounting tolerance and mounting tolerance. (See Non-Patent Document 1 below)
As shown in the cross-sectional view of FIG. 1, the structure of such a conventional light receiving element (PD) includes an n-type semiconductor layer 2 and a light absorption layer 3 made of an i-type semiconductor on the surface side of a PD substrate 1. , P-type semiconductor layer 4 and anode electrode 5 are laminated in this order to form a photodiode, and two cathode electrodes 6 are provided on n-type semiconductor layer 2 on both sides of light absorption layer 3. I have.

  On the back surface of the PD substrate 1, a lens 8 as an optical component is formed by etching or the like so as to align the optical axis with the photodiode, and the incident light 7 passes through the lens 8 from the back surface side of the PD substrate 1. And converges and enters the photodiode. An AR film 9 is laminated on the back surface of the PD substrate 1 as an anti-reflection film, and also covers the surface of the lens 8 to prevent reflection of incident light on the lens surface.

S.R.Cho et al, Enhanced Optical Coupling Performance in an InGaAs Photodiode Integrated With Wet-Etched Microlens, MARCH 2002 IEEE POTONICS TECHNOLOGY LETTERS Vol.14, No.3, p.378-380

  However, in manufacturing such a conventional light receiving element, not only a process of forming a lens in a back surface process is necessary, but also a PD formed on a front surface of a semiconductor substrate and a lens processed on a back surface are mutually separated. However, there was a problem that the alignment was required. Specifically, it is necessary to read the position of a marker or the like formed on the front surface of the semiconductor substrate in accordance with the PD, and then determine the position of the pattern forming the lens on the back surface.

  Therefore, in the conventional manufacturing process of the light receiving element, an expensive stepper capable of aligning (aligning) both surfaces of the substrate, a wafer support system for performing the back surface process, and other devices not required in the normal PD manufacturing process. Has to be used, and there is a problem that the manufacturing cost increases.

  The present invention has been made in view of the above-described conventional problems, and an object of the present invention is to manufacture a light-receiving element having a structure capable of reducing a decrease in optical coupling efficiency and a decrease in mounting tolerance even when a bonding area is small. In doing so, by eliminating the need for alignment between the lens and the PD, which has been required conventionally, the number of processes and the number of devices used are reduced, and a light-receiving element having high-speed response characteristics that can be manufactured at low cost is provided. is there.

In order to solve the above-mentioned conventional problems, the invention described in one embodiment is directed to a light receiving element including a semiconductor substrate having a photodiode and a lens formed adjacent to the photodiode on a first surface. In the semiconductor substrate, a second surface facing the first surface is processed to reflect light incident on the semiconductor substrate into the substrate, and a side surface of the light receiving element is A light receiving element characterized by being processed to reflect light incident on a semiconductor substrate into the substrate .

FIG. 13 is a cross-sectional view of a PD which is a conventional light receiving element. FIG. 2 is a cross-sectional view of a PD that is a light receiving element according to the first embodiment of the present invention. FIG. 2 is a plan view of a PD as a light receiving element according to the first embodiment of the present invention.

  Hereinafter, the light receiving element of the present invention will be described in detail.

  In the light receiving element described in the present embodiment, a PD is formed on a surface (first surface) of a semiconductor substrate, a semiconductor lens is formed on a surface of the semiconductor substrate adjacent to the PD, and a back surface (second surface) of the semiconductor substrate is formed. Is a flat reflecting surface that reflects light incident on the substrate into the substrate, and reflects light incident obliquely on the optical axis of the semiconductor lens from the reflecting surface on the back surface to converge it on the PD. It is characterized by having done.

  According to the light receiving element having the above configuration, in order to enable a high-speed response without a decrease in optical coupling efficiency, a light receiving element having a structure capable of reducing a decrease in optical coupling efficiency and a decrease in mounting tolerance even if the bonding area is small. At the time of manufacturing, alignment conventionally required in the backside process is not required, and the number of steps and the number of devices used are reduced, so that a light-receiving element having high-speed response characteristics can be manufactured at low cost.

(Example 1)
Hereinafter, Embodiment 1 of the light receiving element of the present invention will be described with reference to FIGS.

  FIG. 2 is a sectional view of a PD which is a light receiving element according to the first embodiment of the present invention, and FIG. 3 is a plan view thereof.

  In the first embodiment of FIGS. 2 and 3, a PD using an InP (indium phosphide) -based semiconductor is taken as an example, and the PD substrate 1 is a semi-insulating InP substrate 1. This PD can be formed by the following method.

(Surface process: PD formation)
First, an n-type InP layer 2 and a non-doped (i-type) InGaAs layer (light absorbing layer) are formed on the surface of an InP substrate 1 made of high-resistance InP by using an epitaxial growth method such as a metal organic chemical vapor deposition (MOVPE) method. 3) forming a p-type InGaAs layer 4;

  Next, the above-mentioned p-type InGaAs layer 4, non-doped InGaAs layer 3, and n-type InP layer 2 are processed into a mesa type by known photolithography and etching techniques, and then the n-type InP layer 2 and the p-type InGaAs layer 4 are formed. Then, electrodes 6 and 5 that are in ohmic contact with each other are formed to form a photodiode (PD).

(Surface process: lens formation)
Subsequently, the InP substrate 1 is formed into a lens shape in a lateral portion adjacent to the PD on the surface of the InP substrate 1 in a region where the epitaxial layer is entirely etched by using a technique known in Non-Patent Document 1 or the like. The lens 8 is formed by processing.

On the surface of the lens 8, an antireflection film (AR film 9) having a laminated structure of, for example, SiO ₂ / TiO ₂ is formed. As shown in FIG. 3, portions other than the AR film 9 and the electrodes 5 and 6 on the surface of the InP substrate 1 (portions other than the region where the PD and the lens are formed) are covered with a reflective film 12 for confining the incident light 7. Is also good.

(Backside process)
Subsequently, the process proceeds to the back surface process. Unlike the conventional example, the present invention does not require alignment, and can use ordinary process equipment. In the back surface process, first, the back surface of the PD substrate 1 is polished and adjusted to have a desired thickness, and a total reflection film 11 having a stacked structure of SiO ₂ / TiO ₂ is formed on the entire back surface by sputtering or the like.

  Here, the total reflection film 11 may be formed by forming a metal on an insulating film.

  Thereafter, chipping is performed by dicing to complete a light receiving component including the semiconductor lens 8 and PD on the front surface and the total reflection film 11 on the rear surface. In order to confine the incident light 7 more effectively, a total reflection film may be provided on the side surface of the InP substrate 1 generated by chipping.

  As shown in FIG. 2, when the incident light 7 is incident on the lens 8 formed on this chip at an angle inclined to the side opposite to the PD with respect to the substrate surface or the optical axis of the lens 8, the light incident on the substrate is obtained. Is totally reflected by the total reflection film 11 on the back surface of the substrate, then converged in the vicinity of the absorption layer 3 of the PD, and optically coupled to the photodiode with high efficiency to generate a photocurrent.

  For example, assuming that collimated light (diameter: 20 μm) incident at an angle of 60 degrees from the normal line of the InP substrate is used, when the thickness of the InP substrate is 75 μm, the center of the lens and the center of the PD are separated by about 42 μm. I just need. At this time, if the radius of curvature of the lens is 50 μm, the light is condensed to a spot size of 9.6 μm in diameter at the light receiving portion of the PD.

  The light that has not been absorbed by the absorption layer is reflected again by the reflection films 11 and 12 formed on the back, top, and side surfaces of the PD, and is again absorbed by the absorption layer 3. It is also possible to increase the light receiving sensitivity more than the structure.

  In the structure of the light receiving element of the present embodiment, patterning is performed only on the surface of the substrate on which the PD and the lens are formed, and the back surface is only a flat reflection surface. Since it can be manufactured using only process equipment, it contributes to cost reduction.

  In a PD in which a conventional semiconductor lens is monolithically integrated, the position of the lens on the back surface is determined according to the PD on the front surface of the substrate, thus requiring alignment and complicating the manufacturing process. In the above, since the PD and the semiconductor lens can be formed on the same surface, the number of processes and the number of devices used are reduced, so that the manufacturing process can be reduced in cost.

  As described above, according to the present invention, the back surface process is simplified, alignment becomes unnecessary, and the number of processes and the number of devices used are reduced, so that light-receiving elements and light-receiving components having high-speed response characteristics can be manufactured at low cost. Becomes

Reference Signs List 1 PD substrate, semi-insulating InP substrate 2 n-type semiconductor layer, n-type InP layer 3 (i-type semiconductor) light absorption layer, InGaAs layer 4 p-type semiconductor layer, p-type InGaAs layer 5 anode electrode 6 cathode electrode 7 Light 8 Lens 9 AR film 11, 12 Reflective film

Claims (3)

A light-receiving element including a semiconductor substrate having a photodiode and a lens formed adjacent to the photodiode on a first surface,
The semiconductor substrate has a second surface facing the first surface processed to reflect light incident on the semiconductor substrate into the substrate ,
A light-receiving element, wherein a side surface of the light-receiving element is processed to reflect light incident on the semiconductor substrate into the substrate . Light-receiving element according to 請 Motomeko 1 characterized in that it is a total reflection film is formed on the second surface of the semiconductor substrate. A light-receiving element including a semiconductor substrate having a photodiode and a lens formed adjacent to the photodiode on a first surface,
The semiconductor substrate has a second surface facing the first surface processed to reflect light incident on the semiconductor substrate into the substrate,
A total reflection film is formed on the second surface of the semiconductor substrate,
It said first surface, other than the portion where the photo-diode and the lens is formed is the light incident on the semiconductor substrate you characterized in that the processing has been made to reflect within the substrate receiving light elements.

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